1. Field of the Invention
The present invention relates generally to gyroscopic instruments and is more particularly concerned with two-degree-of-freedom, force-rebalanced, flexure-suspended, free-rotor gyroscopes such as are employed, for example, in strapped-down gyroscopic reference apparatus. More specifically, the invention relates to improved torque motor arrangements for providing a rebalancing force.
2. Description of the Prior Art
Typical flexure-suspended free-rotor gyroscopic devices are disclosed in U.S. patents and pending patent applications assigned to Sperry Rand Corporation including:
W. G. Wing--U.S. Pat. No. 2,719,291--"Rate of Turn Gyroscope" issued Sept. 27, 1955, PA1 T. R. Quermann--U.S. Pat. No. 3,529,477--"Gyroscopic Rotor Suspension" issued Sept. 22, 1970, PA1 T. R. Quermann--U.S. Pat. No. 3,557,629--"Pick-Off and Torquing Device" issued Jan. 26, 1971, and PA1 T. R. Quermann--U.S. Pat. No. 3,677,097--"Protective Stops For Flexure Suspended Gyroscopic Rotor" issued July 18, 1972. PA1 T. R. Quermann--Ser. No. 741,916--"Pick-Off, Torquer, and Reference Signal Generator for Free Rotor Gyroscopes" filed Nov. 15, 1976, and PA1 T. R. Quermann--Ser. No. 742,158--"Flexure Suspensions for Free Rotor Gyroscopes" filed Nov. 15, 1976.
These patents disclose concepts typical of the continuing trend in the design of gyroscopic instruments to achieve smaller, less expensive, and more reliable gyroscopic apparatus for employment in flight control and other precision navigation and stabilization applications, as do the following pending patent applications:
Since they deal particularly with direct current torquer arrangements for flexure-mounted gyroscopes, the Quermann U.S. Pat. No. 3,557,629 and his application Ser. No. 741,916 are of certain interest with respect to the present invention.
While some early versions of such gyroscopic instruments have required either separate pick-offs or rotary transformers and resolvers, such elements representing complex and expensive expedients unsuited for use wherever compactness of design is a requisite, Quermann in U.S. Pat. No. 3,557,629 sought to overcome the problems of the prior art in providing an integrated pick-off, torquer, and reference signal generator system for flexure suspended gyroscopes. Pick-off coils are mounted on the instrument housing, thus eliminating the need for expensive resolver apparatus, and second parts of the pick-off are located on the gyroscope rotor drive shaft. The torquing function is made generally integral with the pick-off function, thereby making the configuration relatively more compact in some designs than devices requiring fully separated pick-offs and torquers. However, a large number and complex arrangement of coils is required in the pick-off coil assembly, as well as complex magnetic circuits difficult specifically to design to minimize external flux leakage and, in general, difficult to machine and to assemble. It is also found to be difficult in some applications to eliminate all coupling or cross-talk between torquer and pick-off circuits. More important, it is critical that leakage flux, both internal and external of the gyroscope, which can disadvantageously couple with adjacent magnetic material as well as with the earth's magnetic field, be kept at an absolute minimum.
In the aforementioned pending Quermann application Ser. No. 741,916, many of the problems of the device of U.S. Pat. No. 3,557,629 were overcome to a significant extent in certain applications by integrating the pick-off, torquer, and rotor speed reference signal functions in a single rotating configuration. The three gyroscopic functions are combined in a single coil assembly using a radially magnetized ring located on the gyroscope rotor wheel with a plurality of pick-off coils mounted compactly with respect to the instrument case, each partially inserted in an air gap provided at the gyroscope rotor wheel periphery. The spacial flux variation around the rotor wheel in the air gap generates an alternating current in each pick-off coil as the rotor spins. The difference in the voltages induced in diametrically opposed pick-off coils provides an output signal, while the sum of the signals induced in all coils provides an alternating phase and frequencey reference voltage. Since there is a finite unidirectional magnetic field in the air gap, controlled direct currents may be applied to the pick-off coils for torquing the gyroscope rotor without inducing spurious error signals in the pick-off system.
In some applications, it remains attractive, however, to separate the several electrical functions associated with the flexure-mounted rotor in the interest of minimizing its inertia so as to maximize fully the sensitivity of the instrument, and to provide a cost-effective yet efficient design. Furthermore, in some applications, it is desirable to assure a cost effective instrument by making certain that all parts may be economically made or purchased as non-highly specialized parts. For example, the ring magnets used in the instrument of application Ser. No. 741,916 are radially polarized; while such annular magnets are possible to obtain, they are expensive and are not as readily available as are high intensity annular magnets polarized in the axial direction, such as annular magnets constructed of samarium-cobalt magnetic alloy. In the particular application of a rate gyroscopic instrument for a craft with very high turning rate capability; i.e. on the order of 300 degrees per second, the torquer must be fully capable of exerting correspondingly very high precession torques on the rotor with respect to the instrument case. Samarium-cobalt magnet material is particularly useful because of its very high flux density and high demagnetization capability, permitting higher torque command currents. Furthermore, since the magnetic circuit design of the present torquer minimizes flux external leakage, the flux density across the gap may be substantially increased by use of samarium-cobalt magnets.